Experimental  Study on Pedestrian Merging Flow and  Intersecting Flow

行人匯流和交叉流的實驗研究

Student thesis: Doctoral Thesis

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Award date29 Aug 2018

Abstract

With the development of economy, there are more and more mass events being held in the world. How to ensure large scale pedestrian safety and make mass crowd in good order are great challenges for organizers. In large scale pedestrian movement, merging flow and intersecting flow contain complicated mutual interactions between pedestrians and are easy to lose control. However, there is lack of experimental studies in pedestrian merging flow and intersecting flow.

In this thesis, pedestrian walking characteristics of merging flow and intersecting flow were investigated by a series of well controlled laboratory experiments. Up to 391 people took part in the experiments and each participants’ trajectories were extracted by a mean-shift algorithm. The second chapter describes the movement of single-file pedestrian merging flow. It was found merging angle θ did not affect fundamental diagrams, but fundamental diagram after merging (downstream) was different from that before merging (upstream and the branch) at large densities. The flow before merging had a peak value 1.2 ped/s at the density of 0.9 ped/m and the flow after merging increased with the density up to 1.6 ped/m. A negative exponential function was obtained to fit the density-velocity relation before merging. Moreover, we found that the efficiency of the merging flow increased when a proper metronome frequency was put in the entrances to control the inflow rate. The flow in scenario with θ=120ºwas most efficient considering both Shannon entropy and average time headway.

In the third chapter, we present the results of mass merging crowds. The formation of lanes was observed, the widths of the lanes in the branch were 0.43m±0.04m for density about 3 ped/m2~4ped/m2 and 0.57m±0.09m for density about 2ped/m2~3ped/m2 respectively. Shannon Entropy was used to analyze the utilization of the passage. It was shown that the space usage in merging area was most efficient when the width of the two branches was half of the main corridor. Density and velocity relation in the merging area corresponded with previous studies about unidirectional flow at densities between 2 ped/m2 and 5.5 ped/m2. Moreover, pedestrian flows in the branch and main channel became mutual bottleneck to each other under mass crowd when the branch width was large enough. That is when the width of the branch increased, the flow upstream gradually became smaller and then kept stable, while the flow in the branch gradually became larger and then kept stable. Spatiotemporal diagrams showed pedestrian flow in the branch and upstream had two states: free and clogging. While clogging did not happen downstream due to open boundary. Moreover, density profile showed the density in the merging area was larger than that in other places and density in the corner was largest, which existed potential safety hazard.

The fourth chapter introduces the characteristics of four-directional intersecting pedestrian flow. Density in the cross area reached 10 ped/m2 when pedestrians walked forward directly in the corridor, which was the highest density that had been achieved in experimental study of four directional intersecting flows. The change trend of density curve for each directional flow in cross area varied when the density reached 10 ped/m2 due to nonlinear interaction between pedestrians. In order to adapt the study of fundamental diagram for four directional intersecting flows, a new coordinate system based on pedestrian motion was built to measure local variables. The local density-velocity relation was consistent with previous results obtained from actual high-density pedestrian flow. At high densities, the average local velocity in cross area is a bit larger than previous study. The reason may be due to the density difference between the cross area and the corridors, which can be observed in real life. Velocity field and its corresponding streamlines and contour lines were constructed and analyzed. An efficient rotary traffic pattern was found when people walked on their right hand side along the corridors. Moreover, turbulence intensities in different scenarios were compared and the results implied that putting an obstacle in the center of cross area and pedestrians walking on the right hand side along the corridors improved traffic stability in the cross area.

The study can give some advice for crowd management and pedestrian facility design. Future studies are proposed in the end.